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syntax-tree/unist-util-visit-parents: utility to recursively walk over unist nodes, with ancestral information

unist utility to walk the tree with a stack of parents.

This is a very important utility for working with unist as it lets you walk the tree.

You can use this utility when you want to walk the tree and want to know about every parent of each node. You can use unist-util-visit if you don’t care about the entire stack of parents.

This package is ESM only. In Node.js (version 16+), install with npm:

npm install unist-util-visit-parents

In Deno with esm.sh:

import {visitParents} from 'https://esm.sh/unist-util-visit-parents@6'

In browsers with esm.sh:

<script type="module">
  import {visitParents} from 'https://esm.sh/unist-util-visit-parents@6?bundle'
</script>

import {visitParents} from 'unist-util-visit-parents'
import {fromMarkdown} from 'mdast-util-from-markdown'

const tree = fromMarkdown('Some *emphasis*, **strong**, and `code`.')

visitParents(tree, 'strong', function (node, ancestors) {
  console.log(node.type, ancestors.map(ancestor => ancestor.type))
})

Yields:

strong ['root', 'paragraph']

This package exports the identifiers CONTINUE, EXIT, SKIP, and visitParents. There is no default export.

visitParents(tree[, test], visitor[, reverse])

Visit nodes, with ancestral information.

This algorithm performs depth-first tree traversal in preorder (NLR) or if reverse is given, in reverse preorder (NRL).

You can choose for which nodes visitor is called by passing a test. For complex tests, you should test yourself in visitor, as it will be faster and will have improved type information.

Walking the tree is an intensive task. Make use of the return values of the visitor when possible. Instead of walking a tree multiple times, walk it once, use unist-util-is to check if a node matches, and then perform different operations.

You can change the tree. See Visitor for more info.

tree (Node) — tree to traverse
test (Test, optional) — unist-util-is-compatible test
visitor (Visitor) — handle each node
reverse (boolean, default: false) — traverse in reverse preorder (NRL) instead of the default preorder (NLR)

Nothing (undefined).

Continue traversing as normal (true).

Stop traversing immediately (false).

Do not traverse this node’s children ('skip').

Union of the action types (TypeScript type).

type Action = typeof CONTINUE | typeof EXIT | typeof SKIP

List with one or two values, the first an action, the second an index (TypeScript type).

type ActionTuple = [
  (Action | null | undefined | void)?,
  (Index | null | undefined)?
]

Build a typed Visitor function from a tree and a test (TypeScript type).

It will infer which values are passed as node and which as parents.

Tree (Node, default: Node) — tree type
Check (Test, default: Test) — test type

Visitor.

Move to the sibling at index next (after node itself is completely traversed) (TypeScript type).

Useful if mutating the tree, such as removing the node the visitor is currently on, or any of its previous siblings. Results less than 0 or greater than or equal to children.length stop traversing the parent.

unist-util-is compatible test (TypeScript type).

Handle a node (matching test, if given) (TypeScript type).

Visitors are free to transform node. They can also transform the parent of node (the last of ancestors).

Replacing node itself, if SKIP is not returned, still causes its descendants to be walked (which is a bug).

When adding or removing previous siblings of node (or next siblings, in case of reverse), the Visitor should return a new Index to specify the sibling to traverse after node is traversed. Adding or removing next siblings of node (or previous siblings, in case of reverse) is handled as expected without needing to return a new Index.

Removing the children property of an ancestor still results in them being traversed.

node (Node) — found node
parents (Array<Node>) — ancestors of node

What to do next.

An Index is treated as a tuple of [CONTINUE, Index]. An Action is treated as a tuple of [Action].

Passing a tuple back only makes sense if the Action is SKIP. When the Action is EXIT, that action can be returned. When the Action is CONTINUE, Index can be returned.

Any value that can be returned from a visitor (TypeScript type).

type VisitorResult =
  | Action
  | ActionTuple
  | Index
  | null
  | undefined
  | void

This package is fully typed with TypeScript. It exports the additional types Action, ActionTuple, BuildVisitor, Index, Test, Visitor, and VisitorResult.

Projects maintained by the unified collective are compatible with maintained versions of Node.js.

When we cut a new major release, we drop support for unmaintained versions of Node. This means we try to keep the current release line, unist-util-visit-parents@^6, compatible with Node.js 16.

unist-util-visit — walk the tree with one parent
unist-util-filter — create a new tree with all nodes that pass a test
unist-util-map — create a new tree with all nodes mapped by a given function
unist-util-flatmap — create a new tree by mapping (to an array) with the given function
unist-util-remove — remove nodes from a tree that pass a test
unist-util-select — select nodes with CSS-like selectors

See contributing.md in syntax-tree/.github for ways to get started. See support.md for ways to get help.

This project has a code of conduct. By interacting with this repository, organization, or community you agree to abide by its terms.

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